Q156 / 225 · JEE Main 2002 · Physics

If in a circular coil $A$ of radius $R$, current I is flowing and in another coil $B$ of radius $2 R$ a current $2 \mathrm{l}$ is flowing, then the ratio of the magnetic fields $\mathrm{B}_{\mathrm{A}}$ and $\mathrm{B}_{\mathrm{B}}$, produced by them will be

  • Correct answer
    A
    1
  • B
    2
  • C
    1/2
  • D
    4

Solution

In coil A, B $=\frac{\mu_0}{4 \pi} \frac{2 \pi \mathrm{I}}{\mathrm{R}} . \quad \therefore \mathrm{B} \alpha \frac{\mathrm{I}}{\mathrm{R}}$; Hence, $\frac{\mathrm{B}_1}{\mathrm{~B}_2}=\frac{\mathrm{I}_1}{\mathrm{R}_1} \cdot \frac{\mathrm{R}_2}{\mathrm{I}_2}=\frac{2}{2}=1$

Hence, the correct answer is option: 'A'.

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